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LM139-SP: input negative voltage

Dexter Choi
Expert 2795 points
Part Number: LM139-SP
Other Parts Discussed in Thread: LM139, LM139A, , LM339

Dear Sir,

my customer is considering about negative input voltage.

when negative voltage is applied to the LM139 input terminal during 200us @-1.2V as below picture.

questions.

1.If exceeding Input voltage range(-0.3V to +36V) of the device, Is there a possibility of the device(LM139A) damage?

2.What is the solution when negative Input voltage occurs?

3.When the LM139 input Lead is exposed to a continuous negative voltage environment, does stress accumulation and damage occur?

  • 0
    Guru 272720 points

    Are you talking about the LM139, the LM139A, or the LM139-SP?

    Footnote (5) in section 7.1 of the LM139/LM139A datasheet says:

    Input current flows through parasitic diode to ground and will turn on parasitic transistors that will increase ICC and may cause output to be incorrect. Normal operation resumes when input is removed.

    As long as you can ensure that the diode current is limited to 50 mA, the LM139/LM139A will not be damaged. There is no allowed current for the LM139-SP.

  • 0
    Guru 140200 points

    Hi Dexter,

    I would add an input diode clamp and hysteresis:

    dexter_lm139.TSC

    Kai

  • 0
    TI__Guru 53026 points

    Hello Dexter,

    Please see sections 2.6 to 2.9 of the LM339 family appnote:

     Application Design Guidelines for LM339, LM393, TL331 Family Comparators (Rev. A)

    #1 - The inputs can go up to 36V without damage. But going negative can cause damage and/or false operation of that or other channels.

    #2 - The body diode/junctions start to conduct, and currents flow in the die where they should not. This can lead to improper operation of that or other channels. Depending on the available current, it could also cause SCR-type latch-up. The LM139 family is vulnerable to negative voltages.

    #3 - depends on available current. The datasheet says 50mA, but I am personally uncomfortable with that level...but that's what they used back then.  1.2V is getting to  damage territory. I would limit the current to 1mA or less. Normally this is done with a series resistor (as Kai has shown).

    The circuit as shown can damage the comparator if the amp output glitches negative. Unless you can GUARANTEE the amp output never goes negative, even during power-up and power down, then a series resistor and negative clamp are needed.